Motor control centers, as well as other electrical equipment like switchgear, are equipped with draw-out type protective control devices such as fusible disconnect switches, circuit breakers, and fuse trucks. These control devices are inserted into individual cells or compartments within the center to establish mechanical and electrical contact with bus bars, load and line stabs, or similar electrical terminals.
Due to the size and weight of many control devices, they are usually mounted on a support frame with rails or rollers and slid into position. Generally, a mechanical means such as a levering device is required to engage the primary and secondary terminals of the control device to the load lines of the control center. It is also desirable to control the range of movement through various positions such as Connect, Test, Disconnect and Remove positions, to permit operation, removal, change of fuses, servicing, testing, etc. The control device module may include a pair of upstanding cradle arms that define slots that are engaged by levering arms that are attached to the racking mechanism. The levering arms engage the slots in the cradle arms, and rotation thereof causes the control device to be rolled or slid into engagement with the electrical power load lines in the cell of the control center.
This type of racking mechanism and levering device is well known in the art and is available from several manufacturers. For example, the Square D Company produces a line of DS type circuit breakers which operate in accordance with the above description. While the racking mechanism presently available performs well, it is unnecessarily costly and may include many separate parts that are disposed about the circuit device for performing various interlock functions to assure safe installation, operation, removal, and testing. Some of the levering mechanisms of other manufacturers occupy a substantial amount of space in the control device. Thus, other components and features of the control device are prevented from using this area.
Where there are several control devices stacked together or otherwise arranged, the terminals usually remain energized when any one of the individual control devices is being inserted or removed. The exposed terminals pose a safety hazard. An operator could be severely burned or shocked if the terminals were accidentally touched while installing the control device. Therefore, when a control device is inserted, it is desirable to use a lever mechanism which avoids the exposed terminals to prevent inadvertent contact with the energized terminals.
There is a need for a space-saving lever mechanism using an inexpensive, simple assembly which does not interfere with the other components or operation of the control center and the respective control devices. In view of increasing safety requirements for control centers already in operation which may expose energized terminals, there is also a need for a lever mechanism that safely inserts and removes associated control devices and is flexible in adapting to the control center designs of various manufacture.